With the increasing down-scaling of integrated circuits and the increasingly demanding requirements to the speed of integrated circuits, transistors need to have higher drive currents with increasingly smaller dimensions. Fin Field-Effect Transistors (FinFETs) were thus developed. The FinFETs include vertical semiconductor fins above a substrate. The semiconductor fins are used to form source and drain regions and channel regions between the source and drain regions. Shallow Trench Isolation (STI) regions are formed to define the semiconductor fins. The FinFETs also include gate stacks, which are formed on the sidewalls and the top surfaces of the semiconductor fins.
Due to the high density and the high aspect ratio of the fins and the STI regions, the formations of the semiconductor fins and the STI regions face several problems. For example, the pattern loading effect may result in the profiles and the widths of the semiconductor fins to vary significantly from fin to fin, and from wafer to wafer, resulting in a performance variation in FinFETs.